Regarding the impact of adding calcium on TA, adding calcium hardness generally doesn't have a significant effect on TA levels. The Total Alkalinity and Calcium Hardness are separate measurements that influence water balance differently. However, it's essential to monitor both TA and calcium levels for overall water balance.
To calculate how much more acid to add, it would be helpful to get a reliable TA reading from the spa store or use a reliable water testing kit. Based on that reading, you can calculate the appropriate amount of acid to bring the TA to the desired range. It's important to follow the recommended guidelines and instructions provided by the spa store or the acid manufacturer to ensure safe and effective acid dosing.
Regarding the Silken product, if you're concerned about it potentially raising the pH, it might be best to avoid using it at this time. Instead, focus on balancing the TA and pH levels first. Once those are in the desired range, you can consider using the Silken product if it aligns with your water maintenance goals.
Lastly, it's worth mentioning that switching to the 488 filter and removing the micro clean filter is a decision you've made. Be sure to follow the manufacturer's instructions for proper installation and maintenance of the new filter to ensure optimal filtration and water quality in your hot tub.
Remember, maintaining water balance in your hot tub is crucial for water clarity, equipment longevity, and bather comfort. It's always a good idea to consult with spa professionals or refer to the manufacturer's recommendations for specific guidance based on your hot tub model and the products available to you.